The present invention relates to a process for selectively etching one or more oxide layers on a surface of a substrate, and more particularly, to such a process in semiconductor device fabrication to etch silicon oxides.
In the manufacture of semiconductor devices, oxides of silicon are used in many different forms and for different applications. Dense, thermally grown or chemically deposited oxides may find use as dielectric films and insulating layers. Typical of such oxides is the class of tetraethylorthosilicate (TEOS) derived oxides.
Other less dense forms of silicon oxides are also used in semiconductor device fabrication where planarized insulating layers are desired. Examples of these types of oxides include doped oxides such as phosphosilicate glass (PSG), borosilicate glass (BSG), borophosphosilicate glass (BPSG), and boron or phosphorous-doped TEOS. Spin-on glass (SOG) is another porous oxide which is used, especially where planarization is desired.
Many semiconductor manufacturing processes require selective etching to remove one form of silicon oxide (typically a more porous form such as BPSG) in preference to another silicon oxide (typically a dense form such as TEOS) or other material (such as silicon). Where there is a desire for selective etching of different forms of silicon oxides, typically hydrogen fluoride (HF) is used as the primary etchant. However, wet etching using aqueous solutions of HF is not very selective, etching both dense and more porous forms of silicon oxides at similar rates. The art has moved to the use of vapor phase HF etching processes to achieve greater selectivity.
For example, Bergman, U.S. Pat. Nos. 5,235,995, 5,238,500, and 5,332,445 teaches a vapor etch process using a homogeneous mix of HF and water vapor as the etchant gas. Grant et al, U.S. Pat. Nos. 5,234,540 and 5,439,553, teach a vapor phase etching process using HF and an alcohol or organic acid. Mehta, U.S. Pat. No. 5,635,102, teaches a selective etching process which exposes the silicon oxides to alternating pulses of HF gas and inert gas causing selective etching of a porous silicon oxide layer (BPSG) in preference to a dense silicon oxide layer (TEOS). However, while such processes may be selective, some have resulted in an undesirable non-uniform etching of the oxide layers.
One example of a semiconductor fabrication process which requires selective etching of different silicon oxides is the formation of stacked capacitor structures to be used in storage devices such as high-density dynamic random access memories (DRAMs). Such structures are formed using a large silicon wafer as a substrate. Fabrication of these devices requires not only a highly selective etching process, but also one which uniformly etches the oxide layers across the surface of the wafer.
Accordingly, there remains a need in this art for an etching process for oxides having differing densities which is not only highly selective, but also produces uniform etches.